Small water systems (˜100 connections or less) with ambient arsenic (As) levels of 11-25 ppb might achieve low cost compliance with the new US arsenic limit of 10 ppb by using in-tank arsenic filtration. In-tank filtration (i.e., treatment) utilizes a pump to recirculate arsenic-laden water through a small vessel (i.e. filter cartridge, column) containing commercially available arsenic adsorption media. Theoretical calculations and pilot testing indicate that for small water systems in-tank arsenic removal is substantially more efficient and less costly than conventional arsenic removal approaches primarily because it requires a significantly smaller installation and less operation and maintenance.
On Jan. 22, 2001, the United States Environmental Protection Agency (USEPA) published a revised standard for arsenic in drinking water, lowering the level from 50 μg/L to 10 μg/L (US EPA, 2001) effective January 2006. All community and non-transient, non-community (NTNC) water systems, regardless of size are required to achieve compliance with the new arsenic standard (USEPA, 2003). This regulation represents one of the first rules under the 1996 Safe Drinking Water Act (SDWA) amendments that significantly impacts small and rural water systems. An estimated 3,000 community water systems (CWS) and 1,100 NTNC water systems need to take measures to lower arsenic in drinking water. The USEPA has estimated the annualized cost for public water supplies to install and maintain arsenic-treatment systems to be $195 million/year. Another cost analysis conducted by the American Water Works Association Research Foundation (AWWARF), reported an annualized cost estimate of up to $495 million per year.
EPA has estimated the cost to consumers of small water systems (serving less than 3,300 people) to range from $58 to $327 per household/year. Other estimates are significantly higher. For example, in New Mexico costs to comply with the new arsenic regulation are estimated to be $374 to $436 million/year for capital outlay and between $16 and $21 million/year for operation and maintenance costs. This translates into estimated consumer monthly costs of $38 to $42/month for large systems and $91/month for small systems.
The New Mexico Environmental Department (NMED) Drinking Water Bureau has identified 96 water systems possessing 100 connections or less which exceed the new arsenic standard. In the past, the only water treatment these small water systems have conducted is disinfection, usually involving the addition of sodium hypochlorite or chlorine gas to the water prior to storage/distribution. Systems with water containing more than the new 10 μg/L arsenic level must now install and operate a treatment system for the first time. Available technologies for arsenic removal including fixed bed adsorption, ion exchange, and coagulation/filtration require substantial capital outlays for facility construction and operations and maintenance (O&M).
Cost estimates for a new fixed-bed adsorptive arsenic removal system can be derived from the USEPA cost estimating guidance and in this instance are based on a community having 100 or fewer people equivalent to a design flow rate of 0.02 MGD (million gallons per day) and an average flow rate of 0.01 MGD (USEPA, 2000). This EPA guidance corresponds with a year 2000 study that found the average water use in southwestern cities to be 200 gallons per day per person. Based on the USEPA costing, a community of 100 people would incur capital and O&M costs of approximately $159,020 and $9,026, respectively for a new granular iron media (GIM) arsenic treatment facility. The capital and O&M unit costs are $7.95/gpd (based on 0.02 MGD design flow) and $2.47/1000 gallons (based on 0.01 MGD average flow). A coagulation/filtration (C/F) system would also involve similar capital outlay costs; however, O&M costs would be significantly higher especially for small-scale systems. A C/F system becomes cost effective for water systems treating 0.5 MGD or greater.
Recent improvements in arsenic treatment have focused on the media, despite the fact that the cost of arsenic adsorption media is a minor component of the arsenic removal facility. In the example above the media cost accounts for approximately 5% of the capital cost and 37% of the annual O&M cost. This invention is directed at reducing capital and O&M costs by removing the arsenic while the water is inside the community water storage tank.